Non-thermal plasma-assisted NO storage and reduction over cobalt-containing LNT catalysts

Abstract

Based on their high NO oxidation capacity (NOC) and NO x storage capacity (NSC), cobalt-containing LNT catalysts of the type Co/Ba/Al and Pd/Co/Ba/Al were tested under NO x storage-reduction (NSR) conditions, as well as in an H 2-plasma assisted NSR process. For comparison purposes, a traditional Pt/Ba/Al catalyst was tested under the same conditions. The Co/Ba/Al catalyst exhibited similar catalytic properties to those of the Pt/Ba/Al catalyst when an H 2-plasma was employed in the rich phase to assist reduction of the stored NO x. However, the NO x removal efficiency was greatly depressed by the presence of H 2 O and CO 2 in the feed. Notably, the addition of Pd to the Co/Ba/Al sample greatly lessened the inhibiting effects of H 2 O and CO 2 on plasma-assisted cycle-averaged NO x conversion, this being due to the excellent NO x storage performance of the Pd/Co/Ba/Al sample even in the presence of H 2 O and CO 2. The results of the present study show that by combining the high NO x storage capacity of Pd/Co/Ba/Al in the lean phase with non-thermal plasma-assisted activation of the reductant in the rich phase, high NO x conversion can be obtained over a broad temperature window of 150-350°C.

Non-thermal-plasma-activated de-NO x catalysis

“…This effect was attributed to a decrease in the NOx storage capacity of the Co/Ba/Al2O3 catalyst in the presence of H2O and CO2. The addition of Pd to the Co/Ba/Al2O3 catalyst mitigated the inhibition effect of H2O and CO2 in the plasma-NSR system and increased the stability of that catalyst both with and without the presence of H2O and CO2 [32]. Similar results were obtained on the addition of 2% H2O to the feed during plasma-facilitated NOx storage and decomposition or reduction using CH4 over a H-ZSM-5 catalyst.…”

“…A number of research studies developed a DBD reactor and applied NTP to the rich phase of the NSR process (IPC system) using different catalysts including a perovskite catalyst (LaMn0.9Fe0.1O3) [30] and M/BaO/Al2O3 formulations with M = Mn, Fe, Co, Ni, Cu, Pt [31,32]. In comparison to a Pt/BaO/Al2O3 catalyst, the Pt-free catalysts exhibited higher NOx storage capacity, in the fuel-lean feed containing NO, O2 and an Ar balance at low temperatures (30 -300 °C) but also significantly lower activity in NOx removal step under fuel-rich conditions containing H2 and an Ar balance.…”

“…The low activity of these catalysts in the NOx reduction step was significantly improved by the use of the NTP, attributed to the facile H2 activation during NTP (Table 3Table 3). For example, high NOx conversions (up to 90%) between 150-350 °C using Co/Ba/Al2O3 was reported [32]. The effect of CO was also investigated.…”

A Review about the Recent Advances in Selected NonThermal Plasma Assisted Solid–Gas Phase Chemical Processes

“…Their first inspection concerned the comparison between two cobalt-containing catalysts (Co/Ba/Al and Pd/Co/Ba/Al) and the traditional Pt/Ba/Al catalyst in a H 2 -plasma assisted NSR process; when the H 2 -plasma was used in the rich phase to assist the reduction of the stored NO x , the Co/Ba/Al shown similar catalytic properties than those of Pt/Ba/Al. However, when there was the presence of H 2 O and CO 2 in the feed, the NO x removal efficiency was considerably lowered with these two latter catalysts, while in the case of Pd/Co/Ba/Al an excellent NO x storage performance has been encountered by the authors, thus inhibiting the effect of the presence of H 2 O and CO 2 in the feed [83]. Subsequently, their intent has been testing under the same process, non-thermal plasma-assisted NOx storage and reduction, Pt-free catalysts and, under this purpose, a series of M/Ba/Al (M = Mn, Fe, Co, Ni and Cu) catalysts have been prepared and tested by the authors.…”

“…Zhang and coworkers [83][84][85] performed a deep investigation on non-thermal plasma-assisted NOx storage and reduction (NSR) over Ba/Al lean NO x trap (LNT) catalysts. These catalysts work cyclically, alternating their operation between two conditions, fuel-lean and fuel-rich; indeed, under lean exhaust conditions, characterized by high amount of oxygen, NO x are adsorbed on the catalyst surface while, under rich conditions, NO x reduction takes place as a consequence of the presence of an excess of reductant.…”